The decision by Israel and the United States to delay a massive joint anti-missile exercise has set off a frenzy of speculation as to what the move says about relations between the two allies amid mounting tensions with Iran.

U.S. and Israeli officials confirmed over the weekend that they had delayed until the second half of 2012 what was to have been the largest-ever joint anti-missile exercise, Austere Challenge 12.

Speaking off the record, officials in the United States and Israel confirmed published reports that Iran factored into the decision. But just how Iran factored in they would not say, and they insisted that the overriding factors had to do with preparedness for the exercise and Israeli budgetary concerns.

A Pentagon spokesman, Capt. John Kirby, said in an email that the exercise was canceled for routine reasons of wanting "optimum participation" by both sides.

"It is not at all uncommon for routine exercises to be postponed," Kirby said. "There were a variety of factors at play in this case, but in general, leaders from both sides believe that optimum participation by all units is best achieved later in the year. We remain dedicated to this exercise and naturally want it to be as robust and as productive as it can be."

On background, Israeli and U.S. officials said that "optimum conditions" had to do with defense spending, now the subject of a fierce debate in Israel. Israeli Prime Minister Benjamin Netanyahu is under pressure, after a summer of protests, to increase social safety net spending.

In October, Netanyahu said he would cut defense spending to fund social spending, but last week he reversed course, hiking defense allocations by $700 million.

The fluctuating positions have created uncertainty in Israel's defense establishment, and U.S. officials confirmed an account originally reported by Laura Rozen of Yahoo News that it was Defense Minister Ehud Barak who requested the delay in December.

Critics of the Obama administration were not buying it, insisting that the delay revealed a fissure between President Barack Obama and Netanyahu over how to handle Iran. Some suggested that the Obama administration feared the joint exercise would further ratchet up tensions with Iran. Danielle Pletka, vice president of the conservative American Enterprise Institute, said the announcement fit into a pattern of what she depicted as the Obama administration's overly cautious approach to Iran's aggression, including its threats to shut down the Strait of Hormuz, which would cut off much of the West's oil supply.

"Now they cancel these exercises with the Israelis and make the Israelis say they asked for it," she said. "For the Iranians there is only one message here. That is: 'Our tactics are working!' "

One Israeli report quoted unnamed Israeli officials saying that it was the United States that requested the postponement, although U.S. officials and other Israelis insisted that it was Israel that made the request.

Pentagon officials reached out to journalists Tuesday to reinforce their claim that it was Israel that requested the delay. According to an unnamed senior U.S. defense official cited by The Atlantic's Jeffrey Goldberg, Barak requested the cancellation because he feared the Israeli military lacked the resources to carry it out effectively. The official said that U.S. Defense Secretary Leon Panetta objected, fearing that it would send Iran a signal that Israel and America were wavering.

"Panetta's initial reaction was, 'I don't want to take this off the calendar,' " Goldberg quoted the official as saying. Panetta, the official said, was unwilling to cancel the exercise but agreed to a postponement.

Still, speculation regarding the exercise's postponement reflects worries over whether the United States and Israel are on the same page when it comes to Iran.

There have been reports that Obama is pressing Netanyahu not to strike Iran -- or at least to notify the United States in advance of such a strike. The United States condemned last week's assassination of an Iranian nuclear scientist, a killing that many commentators suggested was carried out by the Israeli Mossad intelligence agency.

One theory circulating in the wake of the postponement of the anti-missile exercises is that Israel may be retreating from close defense cooperation, in part because of the U.S. pressure to coordinate on Iran.

Gen. Martin Dempsey, chairman of the U.S. joint military chiefs of staff, was due to arrive in Israel on Jan. 19 and was expected to again press Israel not to strike Iran.

Eitan Barak, an assistant professor of international relations at the Hebrew University of Jerusalem, suggested that Israel's refusal to commit to notifying the United States in advance of any military plans "could be an exercise to employ pressure on the United States to urge it to act against Iran."

He said that Israel has in the past ratcheted up its defensive posture as a means of pressuring the United States and the West to confront a regional threat. He noted that during the first Gulf War, in 1991, Israel pulled its missiles out of their silos after suffering a barrage of Iraqi Scud missiles. Israel was signaling impatience with the failure of allied forces to take out Scud missile launchers in western Iraq.

"Once the U.S. satellites detected the missiles, the United States took Israel seriously" and started hitting western Iraqi targets, the professor said. "It was a clear signal, if you don't do something, we will."

Meir Javedanfar, an Iranian-born analyst who lives in Israel, said the announcement of the decision to delay the anti-missile exercise could as easily be spun as a tale of closer Israel-U.S. cooperation.

"The preference here is for a negotiated settlement," Javedanfar said. "Nobody in Israel wants Iran to have a nuclear bomb -- this is one of the few nonpartisan issues -- but we are also aware that the war with Iran could have far-reaching consequences, including our relationship with the United States."

The decision to postpone a robust U.S.-Israel show of strength could be tied to signals that Iran is softening its position on negotiations over increasing the transparency of its nuclear program, he suggested. Western nations believe the program is aimed at building a bomb, while Iran insists it is peaceful.

Iran has invited inspectors from the International Atomic Energy Agency to visit its facilities later this month, a key U.S. demand, and the Obama administration reportedly is considering a Turkish offer to broker new talks on the transparency issue.

"The Israeli way of making Khameini sit with Obama is to make it clear all options are on the table," Javedanfar said, referring to the Islamic Republic's supreme leader, Ayatollah Ali Khameini. "The idea is to get Khameini to return to the table with a serious offer."

The decision by Israel and the United States to delay a massive joint anti-missile exercise has set off a frenzy of speculation as to what the move says about relations between the two allies amid mounting tensions with Iran.

U.S. and Israeli officials confirmed over the weekend that they had delayed until the second half of 2012 what was to have been the largest-ever joint anti-missile exercise, Austere Challenge 12.